In general computer usage, logon is the procedure used to get access to an operating system or application, usually in a remote computer. Almost always a logon requires that the user have (1) a user ID and (2) a password. Often, the user ID must conform to a limited length such as eight characters and the password must contain at least one digit and not match a natural language word. The user ID can be freely known and is visible when entered at a keyboard or other input device. The password must be kept secret (and is not displayed as it is entered). Some Web sites require users to register in order to use the site; registered users can then enter the site by logging on.
Logon is also used as a modifier as in "logon procedure." The verb form is two words: to log on.
In UNIX-based operating systems, logon is called login. The procedure is called "the login procedure." and the verb form is: to log in.